Fun With a TC!

Well, Gang, some new data!

First off, the "Oh Well" so-so news:

The 100-400 f/4.5-f/5.6 IS will not AF at either the wider/100mm or the longer 400mm when attached to the Kenko 2x TC on either my 5DC or 30D body. In fact, the camera "knows" the TC is attached, since it limits the displayed/shooting aperture to f/9 at the widest (down from the "native" f/4.5) and then to f/11 at the longest zoom.

This is interesting because, well, it's good to know, and since I'm not a stranger to Manual Focus, well, I'll need to be "mentally prepared" to MF a lot. The not-so-good thing is that the critters around here are on the move a lot and I won't be able to use AI Servo AF with this kit, dang!

It's also interesting because the 24-105 f/4 behaves completely different with the TC, with both bodies -- I still have AF, even though the "effective" aperture is f/8! The camera doesn't "pick up" the info from the TC for this lens, only from the 100-400!

And then, regarding our discussion about IS:

With the 100-400, IS stays on when mounted on the tripod! Believe me, it is noticeably helpful when shooting at the effective/magnified 800mm setting.

As to the 24-105, well, that lens has a "quieter" IS than the longer lens, and even with the TC/210mm view, I honestly couldn't tell if the IS was on. Besides, that is not a combination that I'm likely to use except just for play...I guess I could "read up" on it, but Oh Well...

Well, I hope this little project is of interest and maybe even helpful for some folks!

JeffreyG wrote in post #15632905
Just FYI, the reason the TC changes the lens maximum f/stop value is specifically because it does not change the aperture.

Simple example - suppose you have a 100mm focal length lens with a 50mm aperture. This lens is capable of f/2 since 100mm/50mm = 2.

If you add a 2X TC then the teleconverter changes the focal length to 200mm. But the teleconverter cannot change the aperture so that is still 50mm. So now what is the f/stop?

It is f/4 since 200mm / 50mm = 4.

As CDS noted, when you use a non-reporting teleconvertor the camera will tell you that you can still shoot at f/2, but that is only because the teleconvertor is lying to the camera and telling it that it is still shooting a 100mm lens with a 50mm aperture. But it isn't, the camera is just not being informed by the TC that the focal length changed to 200mm.

Yes, it does change the "aperture". Aperture is just a ratio..focal length/entrance-pupil diameter. What it doesn't change, is the entrance-pupil's diameter.

1Tanker wrote in post #15633394
Yes, it does change the "aperture". Aperture is just a ratio..focal length/entrance-pupil diameter. What it doesn't change, is the entrance-pupil's diameter.

No, you have your terms mixed. The aperture of the lens is the optical diameter of the inlet pupil. It is not the ratio of that hole to the focal length of the lens.

People on this forum (myself included) often use the term 'aperture' in shorthand to mean 'aperture ratio' or 'f stop' but we are not being precise when we do so. I'll grant the very common (incorrect) use of aperture, but that is why I very specifically wrote the first sentence of my post to differentiate between the aperture and the f/stop (or aperture ratio).

These terms get interchanged in discussions like this because, well, we can blame it on the "industry" -- aperture and f-stop are interchanged all the time!

In fact, you never hear a term like "pupil diameter" an any "mainstream" discussions, at least none that I'm aware of. Sure, a "technical" article could (and should) mention it, anyone interested in the technical aspects should be aware of the difference between the f-stop and the aperture pupil diameter, but that's just not been well presented and "enforced" at the mainstream level.

And then, things get interesting in this discussion we're having, in that a TC doesn't multiply the "real" (physical) focal length, but the magnification and the resulting loss of light leads to an "effective" focal length and to an "effective" aperture! So, the f-stop/effective aperture is no longer the ratio between lens aperture diameter and the "real" focal length but between the aperture diameter and the "effective" focal length!

Hopefully this conversation can inform people and clear up some confusion, even though my original post didn't go far enough!

Well, then, new tests and a result!

I did dig out a Better Beamer flash extender, which will focus the "illumination" for longer focal lengths, put things together and got out, and a squirrel kindly showed up to model!

Here is a shot of the "kit", it's blurry 'cause I shot it hand-held with my 5DC:

Looks like quite a flash setup you have there, Tony! Is it as effective as it looks like it would be? Also, do you always just have the flash pointed straight forward, or do you sometimes aim it up to bounce off of overhead foliage (similar to people who shoot indoors bouncing it off a ceiling)?

Tom, I wouldn't bounce it, it's made for outdoors with a 300+ focal length, so I don't think bouncing would work, it's pointed straight forward! I'll have to play around with things more, obviously the "catch lights" in the critters' eyes don't look so good!

Well, another day, and we got some sunshine!

So, a neighborhood cat showed up in the front yard and I figured it would be a good test for my 800mm "effective focal length" and, with the nice light, I was able to get a good exposure at f/11 and 1/200 shutter speed (ISO 200), so the flash stayed off!

Remember, I'm "stuck" with manual focus, which adds to my "IQ concerns" when I combine that with the 2c TC, but Oh Well, maybe with practice I can at least "optimize" my results!

If you want to skip to my "page" with a few more pics, go ahead:

http://www.pbase.com …th_long_reach_f​eb_23_2013

I don't want to clutter things up with a ton of photos, but for those who enjoy "pixel peeping" and are wondering about the "IQ effect" of the TC, here is one shot I've cropped and made some Lightroom adjustments to, including a light "going over" the cat with a local Sharpening brush, and over the busy background with a Softening brush:

Well, this afternoon there were some little birds in an apple tree at least 10 yards away, good "subjects" for my 800mm "reach".

And then, they were mostly backlit by the afternoon sun with a bright overcast sky in the background, and therefore "fodder" for my flash extender!

Here's a shot I took without the flash:

Well, I hope I'm not boring you all, but it's been fun!

No photos today, but what do you think so far of the output of my "revamped gear"?